Mechanical Properties and Fracture Toughness Prediction of Ductile Cast Iron under Thermomechanical Treatment

Abstract

Temperature has a great influence on the mechanical properties of ductile cast iron or nodular cast iron. A thermomechanical treatment was carried out at various elevated temperatures of 450 °C, 750 °C and 850 °C using a universal testing machine with a tub furnace. Specimens were held at these temperatures for 20 min to ensure a homogeneous temperature distribution along the entire length of the specimen, before a tensile load was applied. Specimens were deformed to various levels of uniform strain (0%, 25%, 50%, 75%, and 100%). These degrees of deformation were measured with a dial gauge attached to a movable cross plate. Three strain rates were used for each specimen and temperature: 1.8×10−4 s−1, 9×10−4 s−1 and 4.5×10−3 s−1. A simple analytical model was extracted based on the CT tensile test geometry and yield stress and a 0.2% offset strain to measure the fracture toughness (JIC). To validate the analytical model, an extended finite element method (XFEM) was implemented for specimens tested at different temperatures, with a strain rate of 1.8×10−4 s−1. The model was then extended to include the tested specimens at other strain rates. The results show that increasing strain rates and temperature, especially at 850 °C, increased the ductility of the cast iron and thus its formability. The largest percentage strains were 1 and 1.5 at a temperature of 750 °C and a strain rate of 1.8×10−4 s−1 and 9×10−4 s−1, respectively, and reached their maximum value of 1.7 and 2.2% at 850 °C and a strain rate of 9×10−4 s−1 and 4.5×10−3 s−1, respectively. In addition, the simple and fast analytical model is useful in selecting materials for determining the fracture toughness (JIC) at various elevated temperatures and different strain rates.

Multi Response Modelling and Optimisation of Copper Content and Heat Treatment Parameters of ADI Alloys by Combined Regression Grey-Fuzzy Approach

“…Nodular cast iron has been intensively researched, with the main focus on improving its mechanical properties. This can be achieved by suitable heat treatment or by alloying with various alloying elements [1,2]. Ductile iron has good physical, mechanical, and technological properties that lead to rapid production growth such as surface-hardening ability, corrosion resistance, favourable strength, a high modulus of elasticity, and good castability, etc.…”